1. Field of the Invention
The present invention relates to a dowel including an anchor rod provided at its front, in a setting direction, end with a head portion widening in the setting direction, and a sleeve having a through-bore and axially displaceable along the anchor rod, with the sleeve having, at its end adjacent to the head portion an expansion region formed of a plurality of expansion tabs separated from each other by substantially axially extending slots and radially expandable upon a relative displacement of the sleeve and the anchor rod.
2. Description of the Prior Art
With the dowels of a type described above, the anchoring principle is based essentially on a forcelocking connection of an outer surface of the expansion region of the sleeve with the wall of a bore into which the dowel is inserted. This principle is well known and is widely used in conventional expansion anchors. In another type of the dowel described above, the anchoring is based on a formlocking principle, when radially expandable expansion tabs, which form the expansion region of the sleeve, form a formlocking connection with an undercut formed in the bottom region of a bore, into which the dowel is inserted, by cutting elements provided at free ends of the expansion tabs upon the radial expansion of the tabs. Such dowels are known as undercut self-cutting dowels or expansion anchors. Both types of dowels include an anchor rod with a head portion widening in a setting direction, and load application means provided at the rear end, mostly in form of an external thread. The dowel further includes a sleeve mounted on the anchor rod and axially displaceable therealong. The sleeve has an expansion region adjacent to the head portion, with the expansion region being formed, as it has already been mentioned above, by expansion tabs separated by a longitudinally extending slots. Upon displacement of the sleeve over the mostly cone-shaped head portion widening outwardly, the expansion tabs expand radially and provide for anchoring of the dowel in a bore, by forming a force-and/or formlocking connection with the bore wall.
The anchor rod of the known dowel is usually surrounded by the sleeve over a substantial part of its longitudinal extent in the bore. The purpose of the sleeve is not only provide for a radial expansion of the expansion region of the sleeve and for anchoring of the dowel upon its displacement relative to the anchor rod. The sleeve should also transmit the transverse forces, which are generated upon the static and dynamic loading of the dowel, in a direction toward the bore wall. Also known are dowels or expansion anchors in which the expansion region is provided on a relatively short front sleeve which is adjoined by a second sleeve extending up to the bore opening. The second sleeve serves for transmitting transverse forces, which are generated upon the static and dynamic loading of the dowel, to the bore wall.
Bores often have, upon being drilled, a shape that deviates from a theoretical cylindrical shape. In most cases, the bore has a slightly conical shape with the diameter of the bore being larger at the bore opening than at the bore bottom. When bores are formed in concrete, in particular, in a concrete with hard additive, e.g., in french or british flint concrete, there is a danger that a drill, upon striking a hard lump, would temporarily deviate from its line of symmetry. As a result, a bore could be formed which, in addition to a clonicity, would have an arcuate contour. The sleeves of the conventional expansion anchors and of the undercut self-cutting dowels and anchors lie non-uniformly on the walls of such bores. With a cylindrical outer contour of the sleeve, the outer diameter of the sleeve should correspond to the diameter of the bore in its deepest point because otherwise difficulties can arise upon setting of the dowel into a bore. Therefore, the sleeve has a clearance with respect to the bore wall along a substantial portion of its longitudinal extent in the bore. As a result, the sleeve does not adequately lie on the bore wall. This adversely affects transmission of the transverse forces, which are generated upon loading of the dowel, to the bore wall, and negatively act on the dynamic suitability of the dowel. An arcuate contour of the bore can result in increase of the drive-in forces during setting of the dowel. With undercut self-cutting dowels or anchors, which are driven-in with a rotatable sleeve in order to form an undercut in the bore wall upon the radial expansion of the expansion tabs, an increased friction losses can occur between the sleeve wall and the bore wall. The resulting increase in drive-in forces negatively influences the setting speed and can lead, in some cases, to a non-complete anchoring of the dowel.
Accordingly, an object of the present invention is a dowel of a type described above in which the drawbacks of conventional dowels are eliminated.
Another object of the present invention is a dowel having a high dynamic suitability.
A further object of the present invention is a dowel having low friction losses and requiring small drive-in forces for its setting in a bore.
A still further object of the present invention is a dowel which can be anchored in a bore easily, quickly, and reliably.